Pulverizer classifier



P. LANGSET-MO ET AL 3,038,672

June 12, 1962 PULVERIZER CLASSIFIER s Sheets-Sheet 1 Filed May 25. 1958FIE: l

FIE: E

INVENTOR5 P5252 hmaszrm o -R01F 6: SWAA/JOA/ Z/IYCGai/V Z A/okK June 12,1962 P. LANGSETMQ ET AL PULVERIZER CLASSIFIER Filed May 25. 1958 3Sheets-Sheet 2 i \'Q K 1 INVENTORS I I Pam-w bamsasrno a FICi @934 Klye/g TTORNEYS June 12, 1962 P. LANGSETMO ETAL 3,033,672

PULVERIZER CLASSIFIER a Sheets-Shet 5 Filed May 25, 1958 In: 'I

IL//. \LLUII' INVENTORS Panza (AA/48571910 ROLF 6; SMvm'o/v Ammo/1. 7.WURK United States Patent PULVERTZER CLASSIFEER Peder Langsetmo and RolfG. Swanson, Minneapolis,

Minn, and Lincoln T. Work, Maplewood, N.J., assignors to Strong-ScottManufacturing Company, Minneapolis, Minn, a corporation of MinnesotaFiledMay 23, 19-58, Ser. No. 7 37,345 70mins. c1. Mir-485) Thisinvention relates to new and novel improvements for apparatus for bothpulverizing and classifying matter in a'dry state. Moreparticularly,this invention relates to improved apparatus for realizing a minimumrange of particles of the desired particle size in the dischargeproduct.

In the prior art wherein a classifying plate was mounted adjacent theend wall of the casing in which the pulverizing unit is located :and theperipheral edge of the classifying plate was adjacent the peripheraledge of said casing, there has been experienced a problem with respectto the space in the aforementioned area becoming clogged, especiallywhen particles of a fine mesh size were to be ground. Further, it hasbeen hard to obtain a desired classification of "fines when t heclassifying chamber is located in the same casing asthe grinding chamberwithout having undesirable inter-reactions between the particles in thegrinding section and the classifying section of the mill when both theclassifying plate and the pulverizing apparatus have been mounted on thesame shaft.

One of the objects of this invention -is to provide an improvedpulverizer-classifier capable of pulverizing either hard orsoft'material over a very wide range from thecoarser mesh sizes to theextreme fine particle sizes with a narrow size analysis spectrum.Further, it is an object of this invention to provide a unit having agrinding section that is separated from the classifying section but bothlocated in the same casing, the moving parts of the grinding sectionbeing separately controlled and operated from the moving parts of theclassifying section.

Additionally, it is an object of this invention to provide a unit forpulverizing materials wherein the material acted on in the pulverizingsection is rapidly moved to the classifying section where the coarse areseparated from the fines, the coarse being returned to the inlet end ofthe pulverizing unit and, the fines being moved to a discharge outlet.Still further, it is an object of this invention to provide aclassifying section wherein a nonperforated rotary classifying plate isprovided, said classifying section being adjacent thepulverizingportions of v the unit. The classifying plate is providedwith means mounted thereon to induce turbulence in the outer whirl ofthe particles adjacent the periphery of the casing, that is, theboundary layer circulating adjacent said periphery; and to aid inimparting a tangential component to the coarse particles to move theminto a, tailings conduit to be returned to the grinding section.Additionally, the classifying plate is provided with classifying meanson the side opposite the .pulverizing section to centrifugally separatethe coarse from the fines and permit the fines to pass therethroug'hinto, the discharge opening.

A still further object of this invention is to provide apparatus of theforegoing character that is highly efficient as far. asoverall powerconsumption-is concerned, that provides for performing combinedpulverizing and classifying functions in a compact unit which affordscompleteaccessibility to allinternal parts in a' -rnaitter of secondsfor inspection, maintenance, cleaning, and that provides for adjustablefeatures whereby the particles size of the discharge product may bevaried.

Other and further objects are those inherent in the 3, i38,672 PatentedJune 12, 1962 invention herein illustrated, described in the claims, andwill be apparent'as the discussion proceeds.

To the accomplishment of the foregoing and related ends, this inventionthen comprises the features hereinafiter fully described andparticularly pointed out in the claims, the following descriptionsetting forth 'in detail certain illustrative embodiments of theinvention, these being indicative, however, of but a few of the variousways in which the principles of the. invention may be employed.

The present invention is an improvement on the pulverizing andclassifying apparatus specified and claimed in the J. H. Haigh and R. C.Rolotf application, Serial No. 616,443, filed October 17, 1956, now U.S.Patent No. 2,939,638. The aforementioned patent and the presentapplication have a common assignee.

The invention is illustrated by reference to. the drawings in which thecorresponding numerals refer to the same parts and in which:

FIGURE 1 is an elevational view of the combined pulverizing andclassifying unit of this invention with the elimination of thepulverizer section drive motor, the pulley driver of said motor, theguideway for said motor and portions of the belts extended around thepulley driver;

FIGURE 2 is a plan view of the apparatus taken along section lines andin the direction of arrows 22 of FIGURE 1, the view additionallydepicting the respective drive means for the pulverizer and classifiersections;

FIGURE 3 is an end view of FIGURE 2, said View showing the classifyingend of the unit;

FIGURE 4 is a side elevational view in part crosssection taken alongsection lines and in the direction of the arrows 4-4 of FIGURE 2 toillustrate the classifying and 'pulverizing sections along with thewater jacket sur rounding the pulverizing section;

FIGURE 5 is a cross-sectional end view taken along the section line andin the direction of the arrows 5-5 of FIGURE 4 showing the back side ofa classifying plate to illustrate the classifying vanes and classifyinglugs mounted thereon, and the water jacket surrounding the pulverizingsection of the unit;

FIGURE 6 shows aside view and a front view of the improved form ofbeater-mounted on a beater plate, said beater being preferably used forpulverizing soft materials;

FIGURE 7 shows a side view and an end View of an addition form ofbeater, said beater being preferably used for pulverizing hard abrasivematerials.

FIGURE 8 is an enlarged fragmentary detailed view, partly incross-section, illustrating the mounting of the classifying plate on theclassifier shaft, the adjacent portion of the pulverizer shaft and axialposition of the tailing outlet relative to said shafts.

Referring now to the drawings, and particularly to the FIGURES l4, thereis illustrated a pulverizingclassifying unit generally designated asIii. The pulverizing-classifying unit has an outer circular casingllthat is supported above base 16 by legs 15 which are bolted to said baseby a mounting bolt 17. The legs are secured to the casing byconventional means such as welding or may be formed integral with thecasing, The casing 11 for the, purposes of the description will beconsidered to be made up of two sections, a pulverizing section 9 and aclassifying section 8. At one end'of the casing 11 and formed integralwith the peripheral edge is a vertical feed end wall 12 which has arectangular feed aperture 21 located in the central portion thereof. Onthe same side'of the mounting base fromtlie casing 11, as the end wall12, a pedestal'or standard 23 is mounted for supporting other'elementsto be described hereinafter.

Formed integral with the casing 1'1 is a feed chute 20 that opens intothe casing at the feed aperture 21 and has a top opening wherein thematerial to be ground is fed therethrough by a worm feed unit generallydesignated as 22; however, it is to be understood that other types offeeders may be used. One end of the aforementioned worm feed unit ismountably secured to the top portion of the feed chute by mounting bolts17 and the other end is mountably secured to the pedestal 23 by support27.

Spaced bearings 24, 25 for journaling a pulverizing shaft 26 therein aresecured to the pedestal by mounting bolts 18. A pulley drum 28 ismounted on the end of the shaft opposite the pulverizing section. Theshaft is rotatably driven by a motor 31, said motor having a pulley drum29 drivingly connected to the drum 28 by belts 30 to cause rotation ofthe shaft. The motor is mounted on the base 16 such that its axis ofrotation is parallel to the axis of rotation of the shaft.

The classifying section 8 is pivotally connected to the outer casing 11on the end opposite the feed chute by a pair of hinges 35, said hingeshaving a lower hinge arm 35b connected to the main casing 11 and anupper hinge arm 35a connected to the classifying end wall 12. Spaceddirectly across the end wall 12 from each of the hinges is a swingablehand wheel 36, each of said swingable hand wheels having a shank 37engageable in a slotted formation or clevis 38 formed integral with theperipheral edge of said end wall.

Secured to the classifying end wall by conventional means (such aswelding) is a generally horizontal support base 41. Mounted on thesupport and secured by U-shaped brackets 53 and bolts 54 are an inboardbearing 42 and an outboard bearing 43, said bearings journaling aclassifying shaft 44. Mounted on the outer end of the classifying shaftis a pulley drum 45 which is rotatably driven by a variable speed pulleydrive system located under the bracket 46. The variable speed drivesystem includes a pulley drum 45 and handle 47, said system beingconventional and therefore will not be further described. The systemunder the bracket 46 is in part mounted on a T-support 52, said supportbeing secured to the mounting base 41. The handle 47 provides a meansfor adjusting the speed of the system.

The motor 48 which drives the variable speed drive system is mountablysecured to the support base 41 by a U-shaped bracket 49, said bracketbeing held in place by conventional means as mounting bolts 50. Themotor is so mounted on the support base that its drive shaft is spacedfrom and parallel to the classifying shaft 44.

The classifying shaft 44 extends inwardly through an outlet aperture 57located in the central portion of the classifying end wall 13. Adischarge housing 58 having a side wall aperture 59 of the same size andshape as the outlet aperture 57 is mountably secured to the classifyingend wall by flat-heated screws 60. In the opposite side wall of thedischarge housing from the side wall aperture, a seal ring 62 secured tothe side wall by bolts 63 is mounted in an opening 61. The seal ring hasan inner opening therethrough which is the size of the shaft, the innerperipheral wall forming said opening having a peripheral groove 64 formounting an O-ring 65 therein. Thus, the seal ring in combination withthe O-ring forms a seal between the shaft and the discharge housing toprevent escape of fines along the shaft. The discharge housing has aflange 58b encompassing the top aperture 580 such that an appropriateconduit (not shown) may be connected thereto to lead to a storage bin.As is conventional a discharge fan (not shown) may be located in saidconduit.

The pulverizer shaft 26 previously mentioned extends inwardly through apulverizing shaft opening 68 located in the central portion of the feedend wall 12, said shaft having a common axis of rotation with theclassifying shaft 44. The inner end of the pulverizing shaft 26 extendssuch that it is adjacent but slightly spaced from the inlet end of theclassifying shaft 44. An annular seal 69 is mounted on the pulverizingopening 68 to form a tight fit between the feed end wall and the outerperiphery of the shaft to prevent the material to be pulverized fromescaping through said opening. A groove 68a is formed in the innerperipheral wall of the seal 69 such that an O-ring 70 may be insertedtherein similarly as for the seal ring mounted on the classifying shaft.

As best observed from FIGURE 4, the pulverizing shaft 26 which extendsinwardly from the feed end wall 12 has an end plate retainer 89 securedthereon adjacent the ring seal 69. This retainer 89 serves to establishthe reference position of the plate which is mounted on said shaft.Since it is desirable that a plurality of spaced disks or beater plates80, 81, and 82 be removably stacked on the shaft 26, the pair of spacers87 are positioned between the several disks. A retainer cap 88 held inposition by a lock washer 86 and a nut 92 on the inner end of the shaft,maintain the stacked relationship of the aforementioned plates duringthe operation of the unit.

Each of the plates 80, 81, and 82 have a plurality of spaced heaters 84mounted on the peripheral edges thereof. Also, each of the plates isprovided with a plurality of annularly located apertures 93 spacedperipherally inward.

Spaced radially inwardly from the heaters 84 and secured to the feed endplate side of the beater plate 80 are a plurality of primary beatervanes a, said heater vanes being axially cooperable with annular reargrinding plate which may be of a corrugated configuration, for primarysize reduction of the material to be ground or pulverized. The heaters84 mounted on the beater plates are radially cooperable with acylindrical liner 91 which may be corrugated. As may be noted in FIG-URE 4 the abutting edges of the annular rear grinding plate and thecylindrical liner have inter-locking edges such that they form a tightfit thus preventing any escape of material at the place of junctionbetween the two aforementioned elements.

On the opposite side of the beater plate 80 from the primary beatervanes 85a are a plurality of secondary beater vanes 85b secured to thebeater plate 80. The beater vanes 85b are similarly spaced as theaforementioned beater vanes 85a. The beater vanes 85b perform twofunctions, that is, they serve to balance the beater plate 80 and at thesame time aid to perform the pulverizing function in conjunction withthe beater plate 81 and thereby yield a better size reduction of thematerial.

As may be best seen in FIGURES 4 and 5 a classifying plate 100 ismounted on the inner end of the classifying shaft 44 adjacent the beaterplate 82.The classifying plate is held in position on the end of theshaft by fastening a classifier hub 97 to one side of the plate and aclassifying plate ring 98 to the opposite side of the plate, there beingcap screws extending through appropriate spaced apertures formed in thehub, the classifying plate, and the classifying plate ring to securesaid elements in fixed relation to one another. The hub 97 along withthe classifying plate attached thereto are axially positionable on theshaft for a purpose to be explained hereinafter.

It may be noted by inspection of FIGURE 4 that the hub 97 issubstantially a sleeve having a taper bore extending therethrough. Thissleeve or hub encircles a split tapered bushing 99 composed of separatehalves 99a and 99b, said hub and split tapered bushing being held inposition by tightening bolts 99d and loosening bolts 990 such as thosedescribed in application, Serial No. 616,443 which has issued as US.Patent 2,939,638 (see lines 53-75 of column 3 and lines 0 to 28 ofcolumn 4 of the printed patent). Only one loosening bolt and onetightening bolt are illustrated, however, a plurality of theaforementioned bolts are provided as described in said patent. Themanner in which the bolts and associate elementsare utilized inadjustable axially positioning the classifying plate is fully set forthin the abovementioned lines of Patent 2,939,638 and therefore will notbe described herein. The split bushing 99 is splined to shaft 44 by akey 102.

Mounted on the peripheral portion of the classifying plate1-0tl are fourspaced elongated lugs 103. Each of these lugs are triangular shaped invertical cross-section and extend longitudinally on either side of theclassifying plate 100. Of course, it is to be understood that either alarger or a lesser number of lugs could be used on the classifyingplate, although we prefer to use between two and four to obtainbest'results. The purpose of these lugs will be described hereinafter.

On the discharge side of the classifying plate spaced radially from theshaft 44 and located approximatelymidway between the shaft and the outerperipheral portions of the classifying plate are a plurality ofclassifying vanes 105. The vanes are positioned between /2 to of theradial distance out from the axis of rotation of shaft 44. If theyarelocated further out, they disturb the classifying zone (in the areaof arrow 140) and if too far in, the coarse are not subjected tosufficient centrifugal force.

As may be noted in FIGURE 5, the flat surface of each vane isperpendicular to the classifying plate and has an elongated dimensionthat is located radially from the axis of rotation of the classifyingplate. Although for fine grindings, we have found that best results maybe obtained with the use of 20-24 spaced classifying vanes, it is to beunderstood that either a larger or lesser number of vanes may be used.The vanes may be attached to the classifying plate by any conventionalmeans such as flat headed rivets 106 as shown in FIGURE 5.

The inner wall of the classifying end plate 13 has a shallow annularrecessed portion 139 formed therein, said recessed portion extendingradially outward from the edge of the outlet aperture 57 to form anannular shoulder 141 adjacent the lugs 103, the purpose of saidstructure will be explained hereinafter.

As may be noted in FIGURE 4, a relatively wide shallow groove 110 isformed in the inner peripheral wall of the outer casing 11. The groovein conjunction with a portion of the outer peripheral wall of thecylindrical liner 91-forms an annular water channel 111.

A hollowed-out water inlet chamber 112 is formed integral with thebottom portion of the casing 11, said inlet chamber having spaced grates113 adjacent to and across the width of the water channel to distributethe water across the width of said channel and to prevent foreignobjects from flowing into the water channel. The side Wall portion 112aof the chamber adjacent the classifying end plate 13 has a threadedaperture 1121) formed therein such that the water inlet pipe 114 may bethreaded into said aperture. Thus water may flow through the pipe intothe hollow portion 112c, pass between the grated sections of saidchamber into the water channel 111.

Formed in the-top of the outer casing and integral therewith is a wateroutlet chamber 118, said water outlet chamber having a top annularflange 118k: and a hollow portion 118:: with spaced grates 113 mountedtherein adja'ce'nt the water channel 111. The width of the hollowportion of 118 'is the same as the width of the water channel, andthence narrows to the diameter of the flange portion. The top innersurface of the flange portion is threaded such that the water outletpipe 119 may be secured therein. Thus, it may be seen that water may bepassed through the inlet pipe 114 to the water inlet chamber where itseparates and flows along both sides of the inner cylinder liner throughthe water channel 111 and upwardly to the water outlet chamber 118 andthence through the water outlet pipe, to provide means for cooling theouter wall of the pulverizing section without having to rely on air flowthrough said section.

Three spaced O-rings are positioned in grooves 120 one of said groovesbeing located adjacent the intersection of the outer casing with thefeed end wall, a central groove being formed adjacent the water channelin the area between the classifying section 8 and pulverizing section 9,and the third groove being formed adjacent the classifying end wall 13.The O-rings 121a, 12112, and 121a are each positioned in the respectivegrooves; the O-rings 121a and 121b forming a water seal on either sideof the water channel. The O-ring 121C provides a seal to prevent thefines from passing out of the casing at the place of intersection of theclassifying end wall with the cylindrical liner and the outer casing.

Referring now in particular to FIGURE 6, a side view and an end view ofour new and improved beater plate 84 are illustrated. The beater plateis made up of a beater section 125 and legs 126. The beater section hasan elongated rectangular face 125a. and is relatively narrow incross-section. Formed integral with the bottom edge of the beatersection are two legs 126, each having a generally flat surface lying ina vertical plane that is perpendicular to a plane passing through therectangular face 125a and having inner faces 126a that are spaced apartfrom each other such that they may be passed over the edge of any one ofthe beater plates 80, 81, or 82. The fiat face of the legs are generallytriangular in shape with the upper apex thereof narrowing to the widthof the bottom edge of the beater portion. Two spaced apertures areformed in the base portion of the generally triangular face in eitherleg such that bolts 128 may be passed through said apertures to securethe beater to the beater plate. Since the slot formed by the two innerfaces 126a of the legs is midway between the length of the beaterportion and both legs are identical in shape and in cross-section exceptthat one leg is rotated 180; the heaters when mounted are balanced suchthat the weight is distributed on either side of the beater plate. Thus,a heater is formed having a substantial impact surface and means forreadily attaching said beater to a heater plate whereby the beater maybe secured to the beater plate and still not disturb the balancethereof.

The heaters 130 shown in FIGURE 7 are quite similar to conventionaltypes already used and there-fore will not be described. It has beenfound that beaters 130 are better for pulverizing hard abrasive materialwhereas the new type heaters 84 shown in FIGURE 6 are superior forpulverizing non-abrasive material.

A tailings conduit .137 having a tailings outlet 136 formed in thecylindrical liner 91 is provided, there being a tailings conduit mountedon either side of the casing. The respective tailings outlets are formedin the cylindrical liner wall on a level that lies in approximately thesame horizontal Zone that the shaft 44 is locatedin, and are located inthe peripheral portion of the casing such that they are adjacent theperipheral edge of the classifying plate. The tailings outlets are madeof a width such that they normally extend on either side of a verticalplane passing through the vertical surfaces of the classifying plate.Mounted in the tailings conduit adjacent the tailings outlet but on theoutside of the casing is a gate valve which is controlled by the handle138. The gate valve 135 is adjustable such that the effective width ofthe tailings conduit may be varied from a fully closed to a fully openedposition.

The tailings conduit 137 extends in an outward direction from thetailings outlet then is bent such that its side walls run parallel tothe casing, said conduit running to the feed end of the casing whereatit is bent in an inward direction. The conduit then extends to tailingsinlet openings (not shown) which are located on either side of the shaft26 and adjacent thereto. Thus, the coarse may be passed from theclassifying section back to and through the feed end wall to be furtherpulverized.

Although the classifying plate with classifying lugs and vanes mountedthereon is described as being used in a beater mill, it is to beunderstood'that it may be used in other comminuting mills to effectuateclassification. Further, it is to be understood that the unit wouldfunction without the provision of a recessed portion in the classifyingend wall as described but the unit would not operate as effectively andthere would be a far greater danger of clogging. In addition, thespacing of any classifying vanes may be varied from each other and fromthe shaft 44, and that the planes of the surfaces of the vanes may beoffset planes extending radially outwardly from the shaft; but it ispreferred that said vanes be located between /2 and of the radialdistance outward from the axis of rotation as previously mentioned.

The structural elements of our new and improved apparatus having beenset forth, a typical operation will be set forth. The exact theory bywhich the present invention operates to effectuate the results obtainedis not entirely under-stood, however, it is believed to be as set forthhereinafter in the description of a typical operation.

Considering now a typical operation, we will assume that all adjustmentshave been made for the fineness desired and that the variou members arein the relative positions pictured in the drawings. The material to bepulverized is advanced through worm feed unit 22 to the inclined chutethrough which it falls into the pulverizing section 9 of the casing 11.As the material enters into the casing 11, it encounters the primarybeater 85a. Centrifugal forces produced by the rotating 'beaters 85adistribute the entering material such that the material is effectivelydispersed between the corrugated back grinding plate 90 and the heaters85a to yield a primary reduction in particle size.

Since the centrifugal forces act upon the larger and heavier particlesmore forcibly than the smaller and lighter weight ones, the greater bulkof the material at this initial stage moves radially outward, only asmall fraction passing to the apertures 93 in the plate 80. Aftersubjection to the action of the primary beaters 85a, the particles arethrown against the cylinder liner wall 91 where they first pass betweenand encounter the heaters 84 on the plate 80. Owing to the presence ofthe liner and attrition between particles more size reduction takesplace. Centrifugal forces will tend to keep the larger particlesadjacent the liner 91, although part of the fines and the coarse will berebounded into the area between the plates 80 and 81 wherein the coarsewill encounter the secondary beater vanes 8512 on the inner side of thebeater plate 80. The latter mentioned vanes will aid in eifectuatingfurther pulverizing action on the coarse material and also to throw saidparticles outwardly against the cylindrical liner. Those particlesremaining next to the liner 91, and of course, those advanced betweenthe heaters 84 are further pulverized to a smaller size. Similarly, thecoarse particles are passed by the heaters 84 mounted on the plate 82where they receive further grinding treatment. The fines are moved in alongitudinal direction through the unit at a faster rate than the coarsedue to the longitudinal air flow through said unit.

The next step is to expose the pulverized material to the action of theclassifying plate 100. Since the classifying plate 100 is driven by themotor 48, and the beater plates 80, 81, and 82 are driven by the motor31, it follows that the speed of the classifying plate is fullyindependent of the pulverizing plates. However, the output whirl of theparticles of the pulverizing section becomes the input whirl of theclassifying section and thus as the pulverized material approaches theclassifying plate, the larger particles are retained adjacent the innerside of the cylindrical liner by centrifugal forces. Where apertures 93have been provided in the beater plates, a portion of the fines may bedrawn therethrough by any air currents that pass through the apertures93 of said plates. Since the classifying plate has no perforationstherein, the air currents carrying both the fines and the coarse have topass around the peripheral edges of said plates. A portion of the coarseparticles adjacent the peripheral wall of the casing will be induced toleave the casing through the tailings outlets to be returned to theinlet end of the pulverize section for regrinding. The main adjustmentsgoverning the quantity of material passing through the tailings conduitsare the axial position of the classifying plate on the shaft, the degreeof closure of the gate valve 135 in the tailings conduit 137, and theadjustments which affect the static air pressure differential in theunit.

As the grinds pass over the peripheral edge of the classifying platethey pass between the rotating lugs 103 which are mounted on saidclassifying plate. The longitudinal lugs tend to impart a component offorce to the coarser particles such that said particles will passthrough the outlet 136 into the tailings conduit to be returned to thefeed end of the pulverizer. Also these lugs tend to stir up and create ahigh degree of turbulence in the boundary suspensional layer that tendsto be formed in the area adjacent the cylinder liner. This action aidsin separating the coarse from the fines, thereby minimizing the quantityof fines passing through the tailings outlet.

The air sweep is sufficiently strong so that the majority of fines and aportion of the coarse are carried over the peripheral edge of theclassifying plate into the area between the end wall and the classifyingplate adjacent the classifying vanes. As may be noted, an annularshoulder M1 is formed on the end wall 13 adjacent the lugs 103, saidshoulder decreasing the effective area between the vertical peripheraledge of the classifying plate and the end wall 13. The provision of ashoulder adjacent the lugs increases radial velocity of the air sweeppassing between said shoulder and the classifying plate and therebyprevents classification from taking place at this point. This has atwo-fold effect, namely, a better separation of grinds may be obtainedand also clogging is prevented from taking place in the aforementionedarea. Also the coarse will be projected off the shoulder and subjectedto classifying action in the free space and will not creep along thewall part in the classifying zone.

The vanes which are mounted on the classifying plate tend to create ahigh degree of turbulence, thus much of the classifying action takesplace in the area between the lugs and the classifying vane. Theclassifying plate is generally rotated at a lower speed than the primaryplate so that a pumping and an inter-Washing action near the outerradial portion of the blades is created. That is, the larger particlesthat come in contact with or close to the blades have a centrifugalforce imparted thereto which throws them in an outward directionadjacent the classifying plate. The larger particles of course will bebrought into the area of the lugs or will be directly thrown to theouter peripheral portion wherein they will enter the tailings outlet dueto the large centrifugal force that is imparted to them. The cross-flowof particles resulting from the coarse and fines being drawn inwardly byair current and the coarse being impelled outwardly by the classifyingvanes tends to set up a circular flow as indicated by the arrows 140.The fine particles of the desired range of sizes will not besignificant-1y effected by the classifying vanes and will be drawntherethrough by the inward air wash to be passed through the dischargehousing 58.

The inward air flow velocity and the centrifugal force acting outwardlyadjacent the classifying end wall is much less than it is in the areabetween the vanes and the wall; but there is still sufficient turbulenceto break the inward movement of the large particles to the dischargeoutlet. The air flow angular velocity at the outer periphery of theclassifying plate is lower than it is adjacent the shaft but the linearvelocity is the same. As a result of the aforementioned factors, bymoving the classifying plate close to the end wall, a sharper cut isobtained.

Also with the vanes mounted such that their edges are adjacent to theclassifying walls, they tend to break up the suspension layer andthereby operate to prevent caking or clogging. Further by mounting thevanes on the back of the classifying plate, a pumping action isobtained,

b said action operating to prevent clogging. However, sufficientdistance has to be left between the classifying end wall and theclassifying plate so that the previously mentioned cross flow may takeplace such as represented by arrow 140.

If the vanes are mounted such that their edges are too great a distancefrom the classifying end wall, poor classifioation is obtained sincemany of the particles escape through the space between the outer edgesof the vanes and said wall without being subjected to proper classifyingaction.

If the vanes used are too large in area, poor classification isobtained. A possible reason is that the vanes tend to operate as a scooprather than to reject the oversize. However, the vanes have to havesufficient radial length to separate the coarse from the fine.

In making adjustments on the unit to vary the product size and/or range,it is preferable not to change the position of the vanes since it isdiflicult to obtain fine control. A small change in the position of thevanes will produce a large change in the product sizes obtained and thusresult in poor classification.

In most cases, the finest of grinds is most conveniently changed bychanging the rate of air passage through the unit and by changing therotation speed of classifying plate. The classifier unit is equippedwith the variable drive located under 46 for making the latteradjustment. By increasing the classifier speed, the larger particleswill be subject to a greater centrifugal force and will be rejected bythe classifier to be returned through the tailings conduit for theregrinding. Various adjustments which may be made to control productsizes are the classifier speed which is inversely proportioned toproduct sizes, the clearance between the beater tip and the cylinderliner, the r.p.m. of the main rotor, the number of beater plates, theamount of grinds recirculated through the tailings return, and the typeof liner-corrugated, smooth, or perforated. The aforementioned factorsare some of the adjustments used to control the degree of fineness ofthe product to obtain the most economical grinding. A more completedescription of the various adjustments and their effect on particle sizeis set forth in US. Patent 2,939,638.

A product with particle size distribution in a narrow spectrum alongwith the most economical grind is usually desirable. A narrow spectrumof particle size is obtained in applicants invention by a highrecirculation rate through the tailings conduit and by using the loosestsetting possible in the grind, thus allowing the particles of anacceptable size to be removed as produced without excessive grinding.The factors contributing to a loose setting are low r.p.m., largeclearance between heaters and liners and a small number of beaterplates.

For tough resilient materials and for fine grinding high speed is usedtogether with small beater-liner clearance. The number of these beaterplates-is kept low as possible, Without getting too coarse a product,and without plugging tailings conduit by too high recirculation rate.The circulation rate may also be governed by using one or both tailingsreturns. Tailingsreturns may be shut olf individually by the gate valvein each of the tailings conduits. For abrasive materials it may bedesirable to use a low grinding speed and maximum number of beaterplates in order to reduce wear on heaters and liners.

Increasing the air flow through the pulverizing section will give acoarser grind, and conversely, a decrease in the air flow will produce afiner grind. Many times, however, air flow is determined by otherfactors, such as conveying velocity. Enough air must move through themill fast enough to convey the amount of material fed and not so fast asto flush the mill without adequate grinding. Another factor indetermining the air flow used in the unit is the amount of air flowrequired for cooling purposes. However, with the use of applicants newand improved water jacket provided for circulation of a cooling fluidaround an outer peripheral portion of the cy1init der liner, the needfor air flow cooling is minimized and at the same time permitting highergrindingspeeds.

As many apparently widely diiferent embodiments of this invention maybemade without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsherein.

What is claimed is:

1. A combined pulverizer and classifier comprising a pulverizing sectionincluding a pulverizing casing provided with an inlet at one end forintroduction of material into the casing and being substantially open atits other end, a first shaft journalled for rotation in said casing,pulverizing means mounted on said first shaft for causing size reductionof material introduced into the pulverizing casing, drive means forrotating said first shaft; and a classifying section including aclassifying casing provided with an outlet opening at one end and beingsubstantially open at its other end for cooperation with the open end ofsaid pulverizing casing, and a second shaft journalled for rotation insaid classifying section, second drive means for rotating said secondshaft, a classifying plate mounted on a second shaft, and means mountedon said classifying plate for classifying the material passing throughthe classifying section, said classifying casing including an end wallhaving an annular shoulder extending inwardly into the interior of theeasing, said shoulder being located adjacent the peripheral edge of theclassifying plate, the outlet opening being formed in the end wall andbeing of a diameter substan tially less than the minimum diameter of theannular shoulder formed on said end wall.

2. A combined pulverizer and classifier comprising a pulverizer sectionhaving a pulverizer casing with an inlet formed in one end and an openended outlet, and pulverizer means rotatably mounted in said pulverizercasing for causing size reduction of material introduced into thepulverizer casing, and a classifying section comprising a classifiercasing having an open inlet end of the same size and shape as the outletend of the pulverizer section so that material pulverized in thepulverizer casing can pass directly into the classifying section, and anend wall on the opposite side of the classifier casing from the inlet,said end wall having a central outlet aperture of a size substantiallysmaller than the classifier casing inlet, a shaft rotatably mounted insaid classifier casing portion concentric with the outlet aperture, saidshaft having an axis of rotation that extends through said aperture, aclassifying plate mounted on said shaft, said classifying plate being ofsubstantially larger size than the size of said aperture, and aplurality of spaced elongated axially extending classifying lugs mountedon the peripheral portion of the classifying plate, said classifyingcasing end wall having an annular shoulder formed on the outerperipheral portion thereof, said shoulder extending into the casing, theinner diameter of the shoulder being substantially greater than thediameter of said outlet.

3. The apparatus of claim 2 further characterized in that a plurality ofspaced vanes are mounted onthe classifying plate, said vanes mounted toextend in a generally radial direction relative to the shaft and locateda suflicient distance outwardly from the shaft to rotate in the generalarea intermediate the shoulder and the outlet.

4. A combined pulverizer and classifier comprising a pulverizer sectionhaving a pulverizer casing with an inlet formed at one end and an openended outlet, and pulverizing means rotatably mounted in saidpulverizing casing for causing size reduction of material introducedinto the pulverizer casing; and a classifying section comprising aclassifying casing having an open inlet end for cooperation with thepulverizer outlet so that the material pulverized in the pulverizercasing can pass directly into the classifying section and an end wall onthe opposite side of the classifier casing from the inlet, said end wallhaving a central outlet formed therein, a shaft rotatably mounted insaid classifier casing, means for driving said shaft independent of therotation of the pulverizing means said shaft having an axis of rotationthat extends through said central outlet, a classifying plate mounted onsaid shaft, said classifying plate being of a substantially larger sizethan the size of said central outlet, a plurality of spaced elongatedaxially extending lugs mounted on the peripheral portion of theclassifying plate to extend axially outwardly of either side of saidplate, said lugs being triangular shaped in cross section and mounted onthe plate to have the apices thereof pointed outwardly of the plate, andelongated classifying vanes mounted on the classifying plateintermediate said shaft and the outer peripheral portion of saidclassifying plate for classifying the pulverized material, each of saidelongated vanes mounted on the plate to extend substantially radiallyrelative to the said shaft and axially closely adjacent to said endwall, each of said elongated vanes being mounted on the classifyingplate a greater radial distance from said axis of rotation than anyportion of the end wall forming said central outlet and a lesser radialdistance than said lugs, said end wall having an annular zone radiallybeyond the vanes that is substantially planar.

5. A combined pulverizer and classifier unit comprising a pulverizercasing with an inlet formed in one end and an open ended outlet at theother end, and pulverizer means rotatably mounted in said pulverizingcasing for causing size reduction of material introduced in thepulverizer casing; and a classifying section comprising a classifiercasing having an open inlet end for cooperation with the pulverizeroutlet so that the material pulverized in the pulverizer casing can passdirectly into the classifying section; and an end wall in the oppositeside of the classifying casing from the inlet, said end wall having acentral outlet aperture formed therein, a shaft rotatably mounted insaid classifier casing, means for driving said shaft, independently ofthe pulverizing means, a classifier plate mounted on said shaft, andclassifying vanes mounted on the classifier plate to extend generallyradially relative to the shaft and axially toward said end wall, theouter axial edges of said vanes being located inwardly of the peripheraledge of the plate a distance substantially A of the outer radialdimension of the plate and inner axial edges located outwardly of theaxis of rotation of the shaft a distance substantially /2 of the outerradial dimension of the plate, said classifier casing having a tailingsoutlet port located closely adjacent the peripheral edge of theclassifying plate, a tailings conduit connected to said port forreturning the tailings from the classifier section to the pulverizersection, and control valve means mounted in the tailings conduit nearthe inlet of the tailings conduit for controlling the flow of tailingsthrough the tailings conduit.

6. A combined pulverizer and classifier comprising a pulverizer sectionhaving a pulverizer casing with an inlet formed at one end, an openended outlet, pulverizer means rotatably mounted in said pulverizercasing for causing size reduction of material introduced into thepulverizer casing; and a classifier section comprising a classifiercasing having an open inlet end for cooperation with the outlet of thepulverizer casing to permit material pulverized in the pulverizer casingto pass directly into the classifier section and an end wall on theopposite side of the classifier casing from the inlet, said end wallhaving a central outlet aperture, a shaft rotatably mounted in saidclassifier casing portion, means for driving said shaft independent ofthe rotation of the pulverizer means, said shaft having an axis ofrotation that extends through said aperture, an imperforate classifyingplate mounted on said shaft, said classifying plate being of asubstantially larger size than the size of said apertures, a pluralityof spaced elongated lugs mounted on the classifying plate close to theinner periphery of the pulverized casing and a plurality of spacedelongated classifying vanes mounted on the classifying plate, said vanesextending radially relative to the shaft and axially outwardly from theclassifying plate toward the end wall, said vanes being located betweenonly /2 and of the distance from the axis of rotation of the shaft tothe peripheral edge of the plate.

7. In a combined pulverizer and classifier, a generally cylindricalcasing having an inlet formed at one end and an end wall at the oppositeend from the inlet, said end wall having a central outlet aperture,pulverizing means mounted rotatably in the inlet end of the casing forcausing size reduction of material, first means for driving saidpulverizing means, a shaft rotatably mounted in the outlet end of thecasing having an axis of rotation and extending through said outletaperture, second means for driving said shaft independent of therotation of the pulverizing means, an imperforate classifying plate of asubstantially larger size than said aperture mounted on said shaft inproximity to the end Wall, and a plurality of elongated radiallyextending classifying vanes mounted on the side of the plate adjacentthe end wall and extending axially within closer proximity to the endwall for classifying the pulverized material as it moves radiallyinwardly to the outlet aperture, said vanes having outer axial edgeslocated a distance radially inwardly of the peripheral edge of the plateabout A of the outer radial dimension of said plate and inner axialedges located a distance radially outwardly of the axis of rotation ofsaid shaft about /2 of the outer radial dimension of the plate, theinterior of the end wall being substantially planar through an annularzone from said aperture to a location a substantial distance radiallyoutwardly of the outer axial edges of said vanes.

References Cited in the file of this patent UNITED STATES PATENTS529,874 Parker Nov. 27, 1894 745,075 Schutz Nov. 24, 1903 938,923 WalkerNov. 2, 1909 1,260,406 Lachmann Mar. 26, 1918 1,628,295 Wickland May 10,1927 1,840,380 Andrews Jan. 12, 1932 1,855,171 Holbeck Apr. 19, 19321,971,314 Lauenstein Aug. 21, 1934 2,042,042 Frisch May 26, 19362,939,638 Haigh et al. June 7, 1960

